This invention relates to graphic processing systems for delivery of character outputs to be displayed or printed and more particularly to a graphic processing system for storage and delivery of characters in the form of pixel unit information and is suitable for high speed processing when developing characters at given positions.
When displaying characters and graphics or figures on a cathode-ray tube (CRT) in the raster scanning manner, a bit map system has been available which employs a memory (bit map memory) adapted to store information corresponding to each pixel of a display unit. This system adopting the bit map memory has also been used to control output signals to a printer. Conventionally, a procedure to issue character and graphic data to the bit map memory has mainly relied upon software which handles a great amount of data, raising a problem of low processing speed. Especially, in a field of high speed generation of graphic figures, hardware is dedicated thereto in some applications but is problematically expensive.
On the other hand, a trend of incorporating the function of generating character and graphic data into an LSI has been propped as reported in publications such as,
(1) "Graphic Display Processor to Integrate Drawing Algorithms and Display Controls" by K. Katsura, H. Maejima et al, Proceeding of Wescon '84, No. 2313, Nov., 1984, and
(2) "Advanced CRT Controller for Graphic Display" by K. Katsura, H. Maejima et al, Hitachi Review, Vol. 33, No. 5, pp 247-255, Oct., 1984.
This LSI implementation permits a remarkable increase in speed of graphic processing at relatively low costs. In addition, the LSI implementation also has a function of copying and transferring information in a rectangular region at high speeds, which function may be applied to a character display. Details of the copying function are proposed by the present inventors in U.S. patent application Ser. Nos. 686,039 filed Dec. 24, 1984 and 727,850 filed Apr. 26, 1985. The system applying the copying function to the bit map character display can afford to greatly promote the processing speed as compared to the prior art system based on software. For example, where 1000 Chinese characters each composed of 24 dots.times.24 dots are displayed in the monochromatic mode, the entire screen can be renewed within about 0.5 to 1 second. In color processing, however, this system faces a problem of degraded performance. Further, the performance of this prior art system is not enough to comply with a needed performance for renewal of the entire screen within about 0.1 second as requested by a field which takes significant account of the man-machine interface.